Multifunctional probe array system

ABSTRACT

A probe array for includes a handle, a first probe and a second probe. The first probe has a first shank, connected to the handle, and a first tip; and the second probe has a second shank, connected to the handle, and second tip. The first tip contains a different material from the second tip. The probe array may be used to write on a surface by contacting the first tip with a surface, where a first ink is on the first tip. This writing method may further include lifting the first tip from the surface and contacting the second tip with the surface.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/234,401, filed Sep. 23, 2005 now U.S. Pat. No. 7,281,419,incorporated herein by reference, which claims the benefit of U.S.Provisional Application Ser. No. 60/719,158, entitled “MultifunctionalProbe Array System”, filed Sep. 21, 2005.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The subject matter of this application may have been funded in partunder a research grant from the National Science Foundation, under NSFGrant Number EEC-0118025. The U.S. Government may have rights in thisinvention.

BACKGROUND

In recent years, scanning probe microscopy (SPM) techniques have beenwidely used for nanolithography applications. The scanning probe in anSPM instrument can be used to modify a surface with nanoscale resolutionthrough direct or indirect approaches. Direct scanning probe lithography(SPL) methods, including dip pen nanolithography (DPN) and scanningprobe contact printing (SPCP), allow deposition of a variety of chemicaland biological materials with high resolution and multi-layerregistration capability. DPN uses a sharp, coated atomic forcemicroscope (AFM) tip to transfer molecules onto a solid surface. It hasbeen used to generate images with feature sizes smaller than 100nanometers (nm). SPCP uses a probe having an elastomeric tip to printimages on a surface. Typically, an ink is first absorbed into theelastomeric tip, and each contact of the tip on the surface transfersthe ink, creating a pixel print. Images can be generated by SPCP in adot-matrix manner.

In conventional probe-based nanolithography, a single probe typically isused for both writing and reading. This creates a risk ofcross-contamination during use. Although it is possible to switch theprobes between writing and reading runs, this practice can beinefficient due to the time required to register the writing and readingprobes with nanometer resolution. For future nanotechnologyapplications, it is desirable to perform a wide variety of differentlithography and microscopy operations without having to switch probesand perform multiple registrations.

SUMMARY

In one aspect, the invention provides a probe array, including a handle;a first probe having a first shank, connected to the handle, and a firsttip; a second probe having a second shank, connected to the handle, andsecond tip. The first tip contains a different material from the secondtip.

In another aspect, the invention provides a method of writing using theprobe array, including contacting the first tip with a surface, where afirst ink is on the first tip. The method may further include liftingthe first tip from the surface and contacting the second tip with thesurface.

In yet another aspect, the invention provides a method of making theprobe array, including forming at least two tip cavities in a substrate;forming a release layer on the substrate and cavities; forming a shanklayer on the release layer; etching the shank layer in at least one tipcavity to form at least one etched cavity; forming a tip in at least oneetched cavity; attaching the shank layer to a handle to form the probearray; and releasing the array from the substrate.

In yet another aspect, the invention provides a method of integrating atleast one scanning probe contact printing probe and at least one dip pennanolithography probe.

In yet another aspect, the invention provides a method of integrating atleast one scanning probe contact printing probe and at least one atomicforce microscopy probe.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic representation of an example of a multifunctionalprobe array.

FIG. 2 is a graph of tip displacement as a function of electrical powerinput for two types of probe cantilevers.

FIG. 3 is a representation of a scanning electron micrograph (SEM) of amultifunctional probe array.

FIG. 4 is a schematic diagram representing sequential operations ofwriting and reading on a surface using an active multifunctional probearray.

FIG. 5 represents a method of making a probe array.

FIG. 6 is a schematic diagram representing an exemplary method of makinga probe array.

FIGS. 7A and 7B are representations of lateral force microscopy (LFM)micrographs of images formed using a multifunctional probe array.

FIG. 8 is a representation of an LFM micrograph of an image formed usinga multifunctional probe array.

FIG. 9 is a representation of an LFM micrograph of a line image writtenby a DPN probe, where the micrograph was generated by a reading probe inthe same multifunctional probe array.

DETAILED DESCRIPTION

The present invention makes use of the discovery that a probe arraycontaining at least two probes having tips of different materials can bea multifunctional array for writing and/or reading images on a surface.It has been found that these multifunctional probe arrays may be used towrite complex images using two or more types of writing tips and to readthe images formed using the same array. Thus, a wide variety of scanningprobe lithography operations may be performed with minimalcross-contamination, improved ease and efficiency of operation, andincreased registration accuracy.

The present invention also makes use of the discovery that probes havingat least two tips made of different materials may be formed in a singlefabrication process on a substrate chip. By forming rigid tips andelastomeric tips in close proximity on a single substrate, these twodifferent types of tips may be integrated into a multifunctional probearray in an efficient and precise manner.

FIG. 1 is a schematic representation of an example of a multifunctionalprobe array 100. Multifunctional probe array 100 includes a handle 110,a first probe 120, and a second probe 130. The first probe 120 includesa first shank 122 connected to the handle 110, and a first tip 124. Thesecond probe 130 includes a second shank 132 connected to the handle110, and a second tip 134. The first tip 124 and second tip 134 are madeof different materials. The array 100 may be used to write an image onsurface 150 and may also be used to read the image on the surface.

The probes 120 and 130 each include a tip, 124 or 134, connected to itsrespective shank. The tip may be positioned at any point along theshank. Preferably the tip is at the distal end of the shank, oppositethe proximal end that is connected to the handle. The materialcomposition of a probe tip can be varied, and is related to the intendedfunction of the probe. AFM reading probes and DPN writing probestypically are made of a rigid material. Examples of rigid materialsinclude semiconductors such as silicon; metals such as permalloy,copper, tungsten, titanium, aluminum, silver, and gold; ceramics such assilicon dioxide, silicon oxide, silicon oxynitride, silicon nitride andtitanium nitride; and polymers such as polyimide, poly(para-xylylene)(‘parylene’), and SU-8 epoxy photoresists. In contrast, SPCP writingprobes typically are made of an elastomer. Elastomers are a class ofpolymers, and examples of elastomers include polysiloxanes, such aspolydimethylsiloxane (‘PDMS’); and polyolefins, such as polybutadiene,polyisoprene and poly(ethylene-co-propylene-co-diene) (‘EPDM’).

Referring again to FIG. 1, a multifunctional probe array having a rigidtip and an elastomeric tip can perform two distinct functions. The probehaving a rigid tip can be used for reading by AFM or for writing by DPN,and the probe having an elastomeric tip can be used for writing by SPCP.Thus, a single multifunctional array can be used to write an image andread the image, or the array can be used to form an image through thecombination of two different types of writing. The distance betweenprobe tips is predetermined and may be accurately maintained through thefabrication process. Since the tip-to-tip distance is known, actionsfrom multiple tips may be spatially coordinated.

The size and shape of a probe tip can be varied. Reading probestypically have sharp tips, such as the point of a pyramid or a cone, toallow for resolution that is as small as possible. Writing probes mayhave a variety of shapes, depending on the feature sizes of the image tobe formed. A sharp writing tip may allow for smaller feature sizes,since the imaging ink is applied at a smaller point on the surface. Ablunt writing tip may allow for larger feature sizes to be writtenrapidly, without the need for multiple applications of the writing tipin close proximity. Examples of writing probe tip shapes includepyramids, cones, wedges, flat-topped pyramids, cylinders, andrectangular prisms. DPN writing probes typically have a sharp point witha curvature radius less than 300 nm, preferably from 200 nm to 1 nm, andmore preferably from 100 nm to 10 nm. A variety of probe tip shapes forwriting or reading are disclosed, for example, in U.S. PatentApplication Publication 2004/0227075 A1, which is incorporated herein byreference.

A multifunctional probe array may include additional probes, each ofwhich independently may be the same as or different from one or both ofthe first and second probes. In one example, a multifunctional probearray includes at least one AFM probe, at least one DPN probe and atleast one SPCP probe. This type of array may write complex images havingtwo or more feature sizes and can read the image produced. This type ofarray may write and read images having two or more distinct substancesat different points within the image. For example, the ink for the SPCPprobe may be different from the ink for the DPN probe.

The probes 120 and 130 each include a shank (122 or 132, respectively)connected to the handle. The shank supports the tip of the probe andconnects the tip to the handle. Examples of typical shank materialsinclude silicon; metals such as permalloy, copper, tungsten, titanium,aluminum, silver, and gold; oxides such as silicon dioxide, siliconoxide, and silicon oxynitride; nitrides such as silicon nitride andtitanium nitride; and polymers such as polyimide, parylene, and SU-8epoxy. The shank may have a variety of shapes, including a cantilever ora rod. In one example, a rectangular cantilever shank has a length from100 to 1,000 micrometers, a width from 10 to 500 micrometers, and athickness from 1 to 10 micrometers. The shank may include shapedelements that allow for an increase or decrease in the flexibility ofthe shank.

The orientation of the shank relative to the handle may be fixed, or itmay be adjustable. A probe having a shank with a fixed orientationrelative to the handle is a passive probe, in which the height of theprobe tip relative to the surface is controlled by the position of thehandle. A probe having a shank with an adjustable orientation is anactive probe, in which the height of the probe tip relative to thesurface can be controlled by changing the orientation of the shankrelative to the handle. Preferably a multifunctional probe arrayincludes one or more active probes. More preferably a multifunctionalprobe array includes active probes that are individually controllable.Arrays including probes having individually adjustable orientations aredisclosed, for example in Zhang, M.; Bullen, D.; Ryu, K.; Liu, C.; Hong,S.; Chung, S.; Mirkin, C. “Passive and Active Probes for Dip PenNanolithography,” First IEEE Conference on Nanotechnology, October28-30, Maui, Hi. (2001), and in U.S. Pat. No. 6,642,129 B2, which isincorporated herein by reference.

The shank of an active probe includes an actuator that changes theorientation of the shank relative to the handle based on a signal,preferably an electrical signal. Examples of actuators that may beintegrated into a shank include electrostatic actuators, piezoelectricactuators, and thermal actuators. In a typical electrostatic actuator, afirst electrode is present on the shank, and a second, oppositelycharged, electrode is separated from the shank by a spacer. These twoelectrodes may generate an electrostatic attraction force uponapplication of an actuation voltage. In a typical piezoelectricactuator, a piezoelectric material is present on the probe shank.Electrically induced mechanical strain may be used to change theorientation of the shank, displacing the probe tip relative to thesurface. This piezoelectric approach is normally used to obtain smalldimensional changes in shank orientation.

Preferably each probe shank includes a thermal actuator. Thermalactuation may offer advantages over other modes of actuation due to itssimplicity of materials, large actuation force, and low voltageoperation. Thermal actuation of probes in an array is disclosed, forexample, in Wang, X.; Bullen, D. A.; Zou, J.; Liu, C.; Mirkin, C. A. J.Vac. Sci. Technol. B 2004, 22(6), 2563-2567. Typical thermal actuatorsinclude two layers of material, where each material has a differentthermal expansion coefficient. In one example, the shank material is oneof the two layers, and the other layer is a resistive heating material.Examples of resistive heating materials include thin film metal layers.Preferably the force on the shank due to the difference in thermalexpansion is sufficient to overcome adhesion forces between the tip andthe surface and to lift the probe tip from the surface.

The shape and configuration of the shank may affect the actuationperformance. FIG. 2 is a graph of tip displacement as a function ofelectrical power input for a rectangular cantilever and for a V-shapedcantilever, each of which include a thermal actuator. The tipdisplacement increased linearly with increasing actuation power for eachshank; however, the V-shaped shank had a larger thermal displacementthan the rectangular shank at same actuation power. The V-shaped shankhad a thinner resistive heater than the rectangular shank, and thus hada higher induced temperature on the shank for the same input power.

The handle 110 may be any material that can connect the probes to acontroller, such as an AFM instrument. Movement of the handle by thecontroller results in translation of the probes in the x-, y- and/orz-direction relative to a surface. For a probe array that includes oneor more active probes, the handle preferably includes one or moreconductive paths connecting the probe actuator(s) to the controller.Preferably, the handle is a semiconductor wafer that includes a separateconductive path for each active probe in the array. This type of handlemay be referred to as a holder chip.

FIG. 3 is a scanning electron micrograph (SEM) of a multifunctionalprobe array 300. This array contained five DPN probes 310, nine SPCPprobes 320, and three reading probes 330 attached to a handle 340 havingindividual conductive paths 350. The inset is an image of a siliconnitride (Si₃N₄) tip 360 with a curvature radius of 100 nm. The DPNprobes 310 had rectangular cantilever shanks and Si₃N₄ tips, each with aradius of curvature of 100 nm. The SPCP probes 320 had rectangularcantilever shanks and PDMS tips having three different sizes. The PDMStips included round tips having a radius of curvature of 300 nm, flattips that were 1 micrometer square, and flat tips that were 5micrometers square. The reading probes 330 had V-shaped shanks and Si₃N₄tips, each with a radius of curvature of 100 nm. The distance betweenadjacent rectangular cantilever probes was 100 micrometers, and thedistance between V-shaped and rectangular probes was 250 micrometers.The tip-to-tip distances may be further reduced to less than 100micrometers, for example, to allow for higher probe density or forcompatibility with a specific SPM instrument. Rectangular and V-shapedcantilevers are typical probe designs used in scanning probe microscopyand lithography. The sharp Si₃N₄ tips may be used to form featuressmaller than 50 nanometers. The blunt PDMS tips may be used to formcoarse features (i.e. micrometer scale) more rapidly than with sharpertips. Multiple tips of the same material and size may offer redundancyor may carry different ink compositions. Since probes 310 and 330 allhave sharp Si₃N₄ tips, their functions may be interchangeable. Forexample, any of the 310 and 330 probes may be used for either DPNwriting or for reading.

FIG. 4 is a schematic diagram representing sequential operations ofwriting and reading on a surface 490 using an active multifunctionalprobe array 400 having two DPN probes 410, two SPCP probes 420, and anAFM probe 430 attached to handle 440. In the array 400, each probe canbe actuated independently. In FIG. 4A, one of the DPN probes has applieda nanometer scale line image 452 to the surface. In FIG. 4B, the twoSPCP probes have applied micrometer scale or sub-micrometer scale dots454 and 456 on either side of line image 452, forming a complete image450. Thus, an image with feature sizes differing bytwo-order-of-magnitude were formed side-by-side using DPN and SPCPprobes in the same array. An image written with a probe array containingat least one DPN probe and at least one SPCP probe may have at least onefeature having a minimum dimension less than 100 nanometers, and atleast one feature having a minimum dimension greater than 400nanometers. Preferably an image written with the probe array may have atleast one feature having a minimum dimension less than 50 nanometers,and at least one feature having a minimum dimension greater than 400nanometers; and more preferably may have at least one feature having aminimum dimension less than 25 nanometers, and at least one featurehaving a minimum dimension greater than 400 nanometers. In FIG. 4C, theAFM probe has scanned the image 450 to read the image.

Writing an image using DPN may include applying an ink to a DPN probetip, and contacting the probe tip with the surface. Image writing usingDPN is described, for example, in U.S. Pat. Nos. 6,635,311 B1 and6,642,129 B2. The application of ink may include any method that resultsin the presence of ink on the tip. Typically, DPN probe tips arecontacted with an ink well to provide ink on the tip. Ink may also beapplied to the tip through a capillary channel in the shank. The use ofcapillary channels for DPN and SPCP probes is described, for example, inU.S. patent application Ser. No. 10/831,944, filed Apr. 26, 2004, whichis incorporated herein by reference. The ink used for SPCP writing maybe the same as the ink used for DPN writing using the array, or the inksmay have different compositions. If multiple SPCP and/or DPN probes arepresent in the array, each probe may have an ink composition that is thesame as or different from any of the other ink compositions on the otherprobes.

Writing an image using SPCP may include applying an ink to an SPCP probetip, and contacting the probe tip with the surface. The application ofink may include any method that results in the presence of ink on thetip. For example, the tip may be contacted with an ink well, with a padcontaining ink, or with a separate probe tip having ink on the tip. Inkmay also be applied to the tip through a capillary channel in the shank.The ink may then be on the entire probe tip, such that contact of thetip with the surface transfers ink to the surface along the entire areaof contact. For tips that are flat, the ink may be present as pixels onthe flat tip if the ink source contained ink pixels. In this example,contact of the tip with the surface may transfer ink to the surface onlyat the pixel locations.

Reading an image using AFM may include monitoring the deflection of theAFM probe as the tip is scanned over the surface while in contact withthe surface. By raster scanning the tip over a sample surface area, alocal topological map may be produced. In a typical AFM reading process,the repulsive force between the surface and the tip causes the shank tobend, and the amount of bending may be determined, for example bymeasuring optical deflection of the shank. A specific example of AFMincludes lateral force microscopy (LFM).

Because the probes are positioned on the handle at predeterminedspacings, the probes do not need to be registered with the surfacebetween each writing and reading step. Instead, the array (i.e. 400,FIG. 4) and/or the surface (i.e. 490, FIG. 4) is displaced laterally bya distance based on the spacing between the relevant probes and thedesired image. Their relative displacement may be achieved by moving theprobe array and/or the surface. In addition, no vertical displacement isnecessary during the process. For a particular writing or reading step,only the probe or probes involved in the step are in a lowered positionto contact the surface. The terms “contact the surface” or “contactingthe surface” each mean that a probe tip is sufficiently close to thesurface to allow ink to be transferred from the tip to the surface, orto allow a force measurement or other measurement that can be correlatedwith a reading signal.

Probes having tips of different materials have not been integratedpreviously, possibly due to the incompatibility of the fabricationprocesses for the various tips. For example, formation of a rigidsilicon nitride AFM tip typically requires plasma enhanced chemicalvapor deposition (PECVD) at 300° C.; but an elastomeric polysiloxaneSPCP tip will degrade at these temperatures. It has now been discoveredthat a mold-and-transfer fabrication technique may allow for multipletip materials and/or multiple tip shapes to be incorporated in onearray. Examples of the materials and processes used in amold-and-transfer fabrication are disclosed, for example, in Zou, J.;Wang, X.; Bullen, D.; Ryu, K.; Liu, C.; Mirkin, C. A. J. Micromech.Microeng. 2004, 14, 204-211, and in U.S. Patent Application Publication2004/0227075 A1.

FIG. 5 represents a method 500 of making a probe array that includesforming at least two tip cavities in a substrate 510, forming a releaselayer on the substrate and cavities 520, forming a shank layer on therelease layer 530, optionally forming an actuation layer on the shanklayer 540, etching the shank layer in at least one tip cavity to form atleast one etched cavity 550, forming a tip in the at least one etchedcavity 560, attaching the shank layer to a handle to form a probe array570, and releasing the array from the substrate 580. The probe arrayincludes a first tip having a first tip material, and a second tiphaving a second tip material different from the first tip material.

Forming at least two tip cavities in a substrate 510 may include forminga mask layer on a substrate and etching the substrate. Examples ofsubstrates that can be used for making a probe array include substratestypically used in semiconductor structure fabrication, such as silicon,germanium, gallium arsenide, gallium nitride, aluminum phosphide,Si_(1-x)Ge_(x) and Al_(x)Ga_(1-x)As alloys, where x is from zero to one.Preferably the substrate is silicon, and more preferably is singlecrystal silicon, such as a {110} single crystal silicon wafer. Forming amask layer on a substrate may include forming a mask layer material onthe substrate and patterning the mask layer materials to expose aportion of the substrate. Examples of mask layer materials includephotoresists, oxide layers such as silicon oxide, and nitride layerssuch as silicon nitride. The mask layer may be patterned by conventionallithographic techniques to form openings in the mask layer materialthrough which the substrate is exposed.

Etching the substrate may include exposing the substrate and mask layerto an etching agent that selectively etches the substrate, with littleor no etching of the mask layer. As the exposed substrate material isremoved at a particular point, a cavity is formed in the substrate. Thesize and shape of the cavity may be determined by the shape of theopening in the mask layer, by the type of etching agent used, and by thelength of time the substrate is exposed to the etching agent. For asingle crystal silicon substrate, it is preferred that the etching agentremoves silicon anisotropically, and it is more preferred that theetching agent removes silicon in a manner that is dependent on thecrystal orientation. For example, if an area of {110} single crystalsilicon is exposed to an etching agent that is crystal orientationselective, then the cavity may have an inverted pyramidal shape. Theinverted pyramid may have a flat bottom corresponding to a {100} crystalplane if the etch time is below a certain threshold, or it may have asharp point if the etch time is above a certain threshold.

Forming a release layer on the substrate and cavities 520 may includeremoving the mask layer from the substrate and forming a layer ofrelease material on the substrate and cavities. The mask layer may beremoved chemically, for example by exposure to a solvent that dissolvesthe mask layer or by exposure to an etching agent that selectivelyremoves the mask layer but not the substrate. The release material maybe deposited directly onto the substrate and cavities, or a precursormaterial may be deposited onto the substrate and cavities, and theprecursor material may then be converted into the release material. Therelease layer may be formed over the entire substrate, or it may beformed in a pattern on the cavities and portions of the substrate.

The release material may be any material that is different from thesubstrate and the shank material. Preferably the release material is notdegraded by the subsequent processing steps until the product is readyto be removed from the substrate. Examples of release materials includematerials that are thermally stable but that can be degraded by contactwith acidic or basic substances. Specific examples of release materialsinclude zinc oxide (ZnO) and aluminum. These materials may be directlyapplied to the substrate and cavities by sputtering. The thickness ofthe release layer may be from 1 nanometer to 100 micrometers, andpreferably is from 10 nanometers to 1 micrometer.

Forming a shank layer on the release layer 530 may include applying alayer of shank material directly, or it may include applying a layer ofa precursor to the shank material and then converting the precursor intothe shank material. Examples of shank materials include silicon; metalssuch as permalloy, copper, tungsten, titanium, aluminum, silver, andgold; oxides such as silicon dioxide, silicon oxide, and siliconoxynitride; nitrides such as silicon nitride and titanium nitride; andpolymers such as polyimide, parylene, and SU-8 epoxy. Preferably theshank material is Si₃N₄, which may be directly applied by physical vapordeposition (PVD) or chemical vapor deposition (CVD), including PECVD.

Optionally forming an actuation layer on the shank layer 540 may includeforming a layer that can contribute to deflection of the shank materialunder an appropriate stimulus. For example, a piezoelectric layer may beformed on the shank layer. In another example, an electrostaticallysensitive layer may be formed on the shank layer. In yet anotherexample, a resistive heating layer may be formed on the shank layer.Preferably an actuation layer is formed on the shank layer. Morepreferably the actuation layer includes a layer of resistive heatingmaterial, and more preferably includes gold or Cr/Au. The actuationlayer may be formed in a pattern on the shank layer, or the actuationlayer may be formed and then patterned. In one example, a resistiveheating material is applied to the shank layer, patterned, and thenoverlaid with another layer of shank material. An overlaid layer ofshank material may help insure that the actuation layer does notdisconnect from the shank during operation.

Etching the shank layer in at least one tip cavity to form at least oneetched cavity 550 may include patterning the shank layer into aplurality of shank shapes. For example, an individual shank shape mayextend from a proximal end to a distal end, where the distal endsurrounds a cavity. The shank shapes may be discrete, or two or more ofthe shank shapes may be connected at the proximal end. Patterning of theshank layer may be performed by conventional lithographic techniques.The pattern of the shank layer after etching includes at least onecavity in which the release layer is exposed. If the tip materials forall the probes are to be different from the shank material, then all thecavities may be etched to expose the release layer.

Forming a tip in at least one etched cavity 560 may include applying atip material to the etched cavity, or it may include applying aprecursor to the tip material to the etched cavity and then convertingthe precursor into the tip material. Excess tip material or precursormaterial may be applied and then mechanically removed from the surfaceof the shank material and/or substrate. A variety of tip materials maybe formed, each material in a different etched cavity. For example,different polymeric tips may be formed by applying different polymers orpolymer precursors to areas surrounding individual etched cavities.Examples of tip materials include silicon; metals such as permalloy,copper, tungsten, titanium, aluminum, silver, and gold; oxides such assilicon dioxide, silicon oxide, and silicon oxynitride; and nitridessuch as silicon nitride and titanium nitride. Examples of tip materialsinclude polymers such as polyimide; parylene; SU-8 epoxy; andelastomers, including polysiloxanes, such as PDMS, and polyolefins, suchas polybutadiene, polyisoprene and EPDM. If the tip material for aparticular probe is the same as the shank material, then the cavity forthe shank does not need to be etched during the etching of the shanklayer 550. In this example, the tip and the shank are integral.

Attaching the shank layer to a handle to form a probe array 570 mayinclude chemically or mechanically attaching the shank layer to thehandle. Chemical attachment includes application of an adhesive layerbetween the shank layer and the handle. Chemical attachment alsoincludes application of a bonding stimulus to the shank layer and handlewhen the layer and handle are in contact. Examples of bonding stimuliinclude heat, electrical current, electromagnetic induction, andvibration. Mechanical attachment includes fasteners, tongue and grooveattachments, and the like.

Releasing the array from the substrate 580 may include treating therelease layer with a reagent that dissolves or degrades the releasematerial. For example, the release layer may be contacted with a solventthat dissolves the release material but that does not dissolve thematerials present in the array. In another example, the release layermay be contacted with an etching agent or an acidic or basic solutionthat preferentially degrades the release material but that does notdegrade the materials present in the array. Preferably the reagent usedto dissolve or degrade the release material does not dissolve or degradethe substrate, so that the substrate and cavities can be used again forformation of another array.

An example of the method of making a probe array is representedschematically in FIG. 6. This product of this example included threedifferent types of probes in a single multifunctional probe array. Eachprobe had a silicon nitride shanks and a tip made either of siliconnitride or PDMS. Each probe in this array could be individuallyaddressed to a surface by thermal actuation. The method of making aprobe array may be used to provide arrays containing a wide variety ofdifferent tip materials, shank materials, and probe actuators.

The following examples are provided to illustrate one or more preferredembodiments of the invention. Numerous variations may be made to thefollowing examples that lie within the scope of the invention.

EXAMPLES Example 1 Fabrication of Multifunctional Probe Array

FIG. 6 represents the method used to fabricate the multifunctional probearray shown in FIG. 3. A {100} single crystal silicon (Si) wafer wasoxidized to form a chip 600 having a layer of silicon oxide (SiO₂) 610on a {100} single crystal Si substrate 620. The SiO₂ layer 610 waspatterned to open small square windows of various sizes in the oxide,and the patterned oxide was then used as an etch mask for the Sisubstrate 620. The chip was treated with a preferential Si etchantsolution of ethylene diamine and pyrocatechol (EDP) at 95° C. The EDPetching of Si was anisotropic and crystal-orientation-dependent. After atimed etch, cavities 612 were formed in the Si substrate 620 bounded by{111} planes. Depending on the etching time and the sizes of openings inthe SiO₂ layer, the cavities ended in a sharp point or had flat bottoms({100} crystal plane). These cavities were used as masters to mold probetips in subsequent processes.

The SiO₂ mask layer 610 was removed by treatment with bufferedhydrofluoric acid, and a thin layer of zinc oxide (ZnO) 630 was thensputtered on the entire substrate 620. Since ZnO is readily etched bymost acids with fast etch rate, it served as a release layer. A thinSi₃N₄ layer (0.2 μm thick) 640 was deposited on top of the ZnO layer.Metal thin films 650 and 652 were then evaporated and patterned to formresistive actuator elements. Another Si₃N₄ layer (0.8 μm thick) 660 wasdeposited and patterned to form probe shanks. The two Si₃N₄ layerssandwiched the metal actuator in between to prevent detachment of themetal films 650 and 652 from Si₃N₄ layer 640. Thermal actuation actionwas achieved by the difference of thermal expansion of the metal and theSi₃N₄ layers.

Two types of probes having tips of different materials were formed on asingle chip 602. For probes having Si₃N₄ tips, the tip was part of theSi₃N₄ layers 640 and 660. These probes were particularly useful for DPNwriting and AFM reading. For probes with PDMS tips, the Si₃N₄ layers 640and 660 were etched to form openings at the distal ends of thecantilevers, exposing the underlying release layer 630. A layer 670 of aliquid precursor for PDMS was deposited on the chip 602, and excessliquid was removed using a rubber blade, leaving PDMS precursor only inthe cavities 612. The chip was then heated at 90° C. for 30 minutes tocure the PDMS.

A handle in the form of a holder chip 680 was fabricated separately andcontained conductive wires. Indium (In) solder bumps 690 and 692 wereelectroplated on both chip 602 and the holder chip 680. The bondingsites provided both electrical connection and mechanical anchoringbetween the probes and the holder chip. Indium was selected as thebonding material due to its low melting temperature (156.6° C.), sincethe presence of cured PDMS tips prohibits the use of processtemperatures above 200° C. The two chips 602 and 680 were aligned andtemporarily bonded together on a contact aligner. The two chips werepermanently bonded in a nitrogen environment by reflowing the indium ata temperature close to its melting point. The final probe array chip 604was released by dissolving the ZnO release layer 630 in sulfamic acid.The probe array chip had 17 tips, including five rectangular DPN probeswith Si₃N₄ tips of 100 nm curvature radius, nine rectangular SPCP probeswith PDMS tips of three different sizes (300 nm round tip, 1 micrometerflat top, and 5 micrometer flat top), and three V-shaped reading probeswith Si₃N₄ tips of 100 nm curvature radius. The distance betweenadjacent rectangular cantilever probes was 100 micrometers, and thedistance between V-shaped and rectangular probes was 250 micrometers.

Example 2 Writing and Reading with Multifunctional Probe Array

Micro and nanolithography tests using the probe array of Example 1 wereconducted on a Thermomicroscopes AutoProbe M5 AFM machine using1-octadecanethiol (ODT) as ink. The ink was coated on the probe tipsusing a contact inking method. A gold-coated silicon chip was used asthe writing surface. The writing surface was mounted on a calibrated,high-precision XY stage, which provided in-plane motions with nanoscaleresolution. The tip-to-tip distances of the probes in the probe arraywere measured using a scanning electron microscope. The probe array wasmounted on the AFM scanning head and brought into contact with thewriting surface. In the lithography process, the XY stage was used todisplace the writing surface by a distance corresponding to the tip andthe desired image spacings for achieving image registration. A widevariety of images were formed with the probe array and were read withthe same array.

FIGS. 7A and 7B are lateral force microscopy (LFM) micrographs ofnanoscale images formed using DPN and SPCP probes of the array. Eachmicrograph is 4 micrometers by 4 micrometers. FIG. 7A is a micrograph ofa line having a width of 20 nm generated by a Si₃N₄ DPN tip, togetherwith a dot having a diameter of 650 nm generated by a PDMS SPCP tip with300 nm curvature radius. FIG. 7B is a micrograph of a line having awidth of 20 nm generated by a Si₃N₄ DPN tip and a dot having a diameterof 1.4 micrometers generated by a SPCP tip with a 1 micrometer×1micrometer flat top. The writing speed for the line images was 0.1micrometer per second, and the tip-surface contact time for the dotimages was 1 minute.

Since the tip-to-tip distance between the different types of probes wasknown, accurate registration between images generated by the differentprobes was achieved. FIG. 8 is an LFM micrograph (5 micrometers by 5micrometers) of a nanoscale image formed using DPN and SPCP probes ofthe array. The lines were generated first using a Si₃N₄ DPN probe. Thesurface was then moved for a predetermined distance corresponding to thedistance between the two tips, and the PDMS SPCP tip was used to printdots on the lines. The dots were 450 nm in diameter with 1 micrometerspacing, and the lines were 40 nm wide with 2 micrometers spacing. Thealignment error between lines and dots was about 50 nm.

With the writing and reading probes in the same array, images generatedby the DPN or SPCP probes could be read immediately after theirformation. FIG. 9 is an LFM micrograph (1 micrometer by 1 micrometer) ofa line having a width of 20 nm generated by a DPN probe, where themicrograph was generated by a reading probe in the same probe array. Noevidence of cross-contamination was found.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that other embodimentsand implementations are possible within the scope of the invention.Accordingly, the invention is not to be restricted except in light ofthe attached claims and their equivalents.

1. A probe array, comprising: means for performing scanning probecontact printing, means for performing dip pen nanolithography, andmeans for forming an image using the means for performing scanning probecontact printing and the means for performing dip pen nanolithography,wherein the means for performing scanning probe contact printing hasradius of curvature of at least 300 nm, and wherein the means forperforming dip pen nanolithography printing has radius of curvature lessthan 300 nm.
 2. The array of claim 1, further comprising means forperforming atomic force microscopy, where the means for forming an imagecomprises means for subsequently reading the image using the means forperforming atomic force microscopy.
 3. The array of claim 2, where themeans for forming an image comprises a handle connected to the means forperforming scanning probe contact printing, to the means for performingdip pen nanolithography and to the means for performing atomic forcemicroscopy.
 4. The array of claim 3, where the means for forming animage further comprises means for individually adjusting the orientationof the means for performing scanning probe contact printing, of themeans for performing dip pen nanolithography and of the means forperforming atomic force microscopy, relative to the handle.
 5. A methodof writing using the array of claim 2, comprising: performing scanningprobe contact printing on a surface to form a first image, performingdip pen nanolithography on the surface to form a second image, andperforming atomic force microscopy to read the first and second images.6. The method of claim 5, where the first image comprises a firstcomposition, and the second image comprises a second compositiondifferent from the first composition.
 7. The method of claim 5, wherethe first image has a first minimum dimension, and the second image hasa second minimum dimension different from the first minimum dimension.8. The array of claim 1, where the means for forming an image comprisesa handle connected to the means for performing scanning probe contactprinting and to the means for performing dip pen nanolithography.
 9. Thearray of claim 8, where the means for forming an image further comprisesmeans for individually adjusting the orientation of the means forperforming scanning probe contact printing and of the means forperforming dip pen nanolithography, relative to the handle.
 10. A methodof writing using the array of claim 1, comprising: performing scanningprobe contact printing on a surface to form a first image, andperforming dip pen nanolithography on the surface to form a secondimage.
 11. The method of claim 10, where the first image comprises afirst composition, and the second image comprises a second compositiondifferent from the first composition.
 12. The method of claim 10, wherethe first image has a first minimum dimension, and the second image hasa second minimum dimension different from the first minimum dimension.13. A probe array, comprising: means for performing scanning probecontact printing, means for performing atomic force microscopy, andmeans for forming an image using the means for performing scanning probecontact printing, and for subsequently reading the image using the meansfor performing atomic force microscopy, wherein the means for performingscanning probe contact printing has radius of curvature of at least 300nm, and wherein the means for performing dip pen nanolithographyprinting has radius of curvature less than 300 nm.
 14. The array ofclaim 13, where the means for forming an image comprises a handleconnected to the means for performing scanning probe contact printingand to the means for performing atomic force microscopy.
 15. The arrayof claim 14, where the means for forming an image further comprisesmeans for individually adjusting the orientation of the means forperforming scanning probe contact printing and of the means forperforming atomic force microscopy, relative to the handle.
 16. A methodof writing using the array of claim 13, comprising: performing scanningprobe contact printing on a surface to form an image, and performingatomic force microscopy to read the image.